Business and consumers use a wide array of wireless devices, including cell phones, wireless local area network (LAN) cards, global positioning system (GPS) devices, electronic organizers equipped with wireless modems, and the like. The increased demand for wireless communication devices has created a corresponding demand for technical improvements to such devices. Generally speaking, more and more of the components of conventional radio receivers and transmitters are being fabricated in a single integrated circuit (IC) package. In order to simplify single chip designs and to make each design suitable for as many applications as possible, much emphasis has been placed on developing direct conversion receivers and so-called “software-defined” radios.
Generally, the demodulation in these radios requires a single multiplication step to recover the transmitted baseband information. A mixer functions as the demodulator. However, a physical mixer also introduces signal leakages among its signal ports (RF input, LO input, and IF output). The signal leakages develop DC-offset levels that change dynamically when the operating environment of the receiver changes. As a result of these impairments, demodulation errors occur.
Many RF receiver designs implement control loops to track and compensate for the unwanted offset disturbances. However, many of these control loops are difficult and expensive to implement in a single integrated circuit package. Many designs require complicated image-rejection filters.
Therefore, there is a need in the art for improved RF receivers that are low cost, high performance and easily integrated into a single integrated circuit chip. In particular there is a need for a RF mixer that minimizes the amount of signal leakage introduced at the RF input port, the local oscillator input port and the intermediated frequency (IF) output port.